This invention relates in general to speed governors for motor vehicles, and in particular to a speed governor advantageous for use with vehicles that have flexible throttle cables.
Many motor vehicles are equipped with speed governors, known as "cruise controls". The cruise control enables the driver to select a speed, which will then be automatically maintained by the control system. One general type employs a servomotor secured to the throttle at the carburetor and connected to a vacuum source of the engine. A vacuum valve opens the vacuum source to increase the vacuum in the servomotor for advancing the throttle. A vent valve selectively bleeds vacuum off, to allow the throttle to retract, it being drawn by its spring. An electrical control circuit senses the vehicle's speed and controls the vent and vacuum valves.
Another type of cruise control employs an electrical servomotor mounted in the passenger compartment next to the accelerator pedal. The electrical servomotor is similarly controlled by a control circuit, but has an electrical motor for moving the throttle.
The vacuum servomotor operates best if the throttle linkage between the carburetor and pedal is a stiff, solid rod. On acceleration, the servo can push the rod rearward, opening the throttle and pushing the accelerator pedal downward. Some vehicles, however, have flexible cables serving as the linkage between the throttle and pedal. On acceleration, there is a danger that the cable will bend or buckle when pushed rearward at the carburetor by the servomotor. The bending might cause the throttle to stick open.
Consequently, on cable throttles, the electrical servomotor mounted at the pedal would be preferable since it pulls the rearward end of the cable to advance the throttle instead of pushing the forward end. However it is more expensive. Mounting a vacuum servomotor at the pedal would have the disadvantage of increasing noise in the passenger compartment because of the operation of the vacuum and vent valves, normally attached to the servo.